(1) Field of the Invention
The present invention relates to a method for in vitro sexual reproduction of corn plants. It is disclosed that the complete developmental sequence of corn from seedling shoot tips to ears with normal ovaries and kernels with viable embryos (i.e. seed to seed) can be achieved using a single set of in vitro experimental conditions. Clusters of ears can also be regenerated from in vitro cultured axillary buds of corn.
(2) Prior Art
There are reports where each stage of corn development was individually achieved in vitro. Corn plants were grown from isolated shoot meristems and flowered in the greenhouse (Irish, E. E., Nelson T. M., Development 112 891-898 (1991). Young tassels (staminate) and ears (pistillate) of corn were also grown to maturity in cultures (Bommeneni, V. R., Greyson, R. I., Am. J. Bot. 74 883-890 (1987); Polowick, P. L. and Greyson, R. I., Can. J. Bot. 63 2196-2199 (1985)). in vitro fertilization of ovaries (Sladky, Z., Havel, L., Biol. Plant. 18 469-472 (1976); Dhaliwal, S., King, P., Theor. Appl. Genet., 13 43-48 (1978)) and development of normal kernels (caryopses) with embryos have also been reported Gengenbach, B. G., Planta 134 91-93 (1977) What is needed is a method which allows the whole sequence of development of corn in vitro.
Corn shoot meristem is temporally and spatially programmed to form various organs (see e.g. McDaniel, C. N., Poethig, R. S., Planta 175 13-22 (1988)). The physiological basic of tassel and ear development in corn is not clear, although the developmental morphology of flower formation has been extensively studied for many years (Irish, E. E., and Nelson, T., Plant Cell 1 737-744 (1989)). Corn inflorescences are first hermaphrodite and later become staminate (tassel) or pistillate (ear) inflorescences by selective suppression of pistils in the terminal tassel and stamens in the axillary ear. Sex expression in plants appears to be controlled by the endogenous growth regulators. Regardless of the photoperiodic requirement, gibberellins synthesized in leaves favor male flower formation while the root-produced cytokinins enhance female flower production. Gibberellin (GA) has been indirectly implicated to female flower development in corn based on the exogenous application and by assay of gibberellins in tassel or ear mutants of corn. Exogenous application of GA did feminize potential tassels (Krishnamoorthy, H. N., and Talukdar, A. R., Z. Pflanzenphysiol. 79 91-94 (1976)). However, unequivocal proof of direct involvement of gibberellins in ear development is lacking (Irish, E. E., and Nelson, T., Plant Cell 1 737-744 (1989)).
There is a need for a method for the in vitro production of different varieties of corn plant which is relatively simple and reliable.